The Origin of Species

Charles Darwin

Chapter III

Chapter IV, page 2

page 1 of 2

How fleeting are the wishes and efforts of
man! how short his time! and consequently how poor will his products
be, compared with those accumulated by nature during whole geological
periods. Can we wonder, then, that nature’s productions should be
far “truer” in character than man’s productions; that they should
be infinitely better adapted to the most complex conditions of life,
and should plainly bear the stamp of far higher workmanship?

Summary

Darwin now focuses on natural selection, returning to
his discussion of a breeder selecting desired characteristics for
animals. If breeders can select characteristics they wish to breed
in their animals and perpetuate these characteristics in their domestic
populations, is it possible for nature to act in the same way? Darwin believes
it is. Variations that give one species an advantage, no matter
how slight, over another species, allow organisms a better chance
of surviving and therefore of leaving more offspring. While breeders
can select variations that are beneficial for them, omniscient nature
has the power to develop and select variations that are imperceptible
to man and beneficial to species in ways that man might never have
considered. Nature can make any slight advantage increase an organism’s
likelihood of surviving over another, and since these advantageous
variations are heritable, they can be perpetuated in future generations.
Conversely, nature can also limit species by not bestowing
advantageous characteristics on them, therefore making the species
less likely to survive and putting them at risk of extinction.

Darwin gives a number of examples of variations that could
be advantageous to an individual organism, passed along to subsequent
generations, and preserved in the future of the species. For instance,
a wolf with slimmer features might be able to run faster and therefore
to escape from its predators. A bear might be born with the instinct
to pursue a more abundant type of prey, which will be easier to
obtain than less abundant types. In a more complex case, a plant
might contain a sweet nectar or colorful petals that attract more
insects than other plants attract, which will spread the plant’s
pollen more frequently. Similarly, an insect might inherit a smaller
body type, allowing it to obtain food more easily from a plant.

Adding to the concept of natural selection, Darwin briefly
outlines the concept of sexual selection, which is another factor
in species evolution. Because having offspring is key to species’
survival, male individuals with variations that allow them to successfully attract
females are more likely to reproduce and therefore to produce more
offspring than others. These advantageous sexual characteristics
are also variations that would be passed on to offspring. Darwin
gives examples of tactics that species of male birds use to attract
females: singing to their potential mates, displaying various brightly
colored feathers, and performing antics to attract attention. If
any variation in these characteristics were to give male birds a
better chance of mating, that variation would likely spread to the
birds’ offspring and, as a result, would become predominant in the
population in subsequent generations. Variations of this sort, such
as color, aptitude for singing, or ornamentation, may have no direct impact
on the ability of an individual organism to survive in nature; rather,
the variations’ utility in helping an organism reproduce is what
allows these variations to be selected and perpetuated in a species.

Darwin goes on to explain the geographical requirements
for the propagation of advantageous traits, noting that isolation
is key to natural selection, as it creates a situation in which
few individuals live in a specific area in which no new organisms
will be introduced. In isolated areas, variations that allow organisms
to survive in that particular environment win out over disadvantageous
ones. In time, these variations spread throughout the species, making
the organisms appear perfectly adapted to their environment. The
workings of natural selection in geographical isolation explain
why floral and animal life is unique in island environments. On
the other hand, large geographical areas in which plant and animal
populations are not isolated allow species to spread and propagate
widely, increasing the species’ numbers and its overall chances
of survival in a range of environments.

Finally, Darwin relates the concept of natural selection
to divergences of character and the gradual creation of new species,
thus explaining the origin of species. As particular variations
are selected over others, these variations lead to a divergence
in characteristics from the parent species. Additional variations
then lead to more divergences, and as some variations propagate
and expand, others die out as a result of the struggle for existence
and the limits of population growth. Darwin provides a chart to
illustrate this process, demonstrating how these divergences create
“branches” of related species. Some branches end as species become
extinct, while other branches multiply as more subspecies develop
and a new species becomes a parent species. Eventually the divergences
become so great that new species come about. Darwin says this process
can take tens of thousands of years.

Analysis

Chapter IV is perhaps the most important chapter in The
Origin of Species, because it lays out the principle of
natural selection, on which Darwin’s theory of evolution is based.
Darwin does not answer every question about the origin of species
in his theory. For example, he does not explain how variations actually
occur in a species population. He simply assumes that new variations
in organisms must be proven to be advantageous and that, over time,
they change the characteristics of the species. How these variations
occur remained a mystery until Hugo de Vries discovered genetic
mutation in 1903. Additionally, Darwin’s
explanation of how variation leads to the creation of species is
not based on clear evidence, because the distinction between varieties
and species had not yet been defined. The holes in his theory, however,
do not take away from the brilliance of his identification of natural
selection as the mechanism for evolution. Significantly, Darwin
answers the question of how species become so well adapted to their
environment without relying on environmental adaptation. With natural
selection, a species’ adaptation to its environment occurs through
a hereditary process—a concept that would eventually connect Darwin’s
evolutionary theory to discoveries in genetics and genetic mutation
in the twentieth century.

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